Prosecutors are seeking the death penalty against Holmes, who is accused of opening fire in a packed movie theater during a July 2012 midnight showing of the latest Batman installment, "The Dark Knight Rises."

Authorities have said Holmes was dressed head to toe in protective gear.

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He allegedly threw tear-gas canisters in the theater and then opened fire on the patrons, according to witnesses. Police say he used several weapons, including an AR-15 rifle, before fleeing the theater.

Outside the theater, the shooter was apprehended, identifying himself to police as "The Joker," one of Batman's archenemies.

He faces 166 charges tied to the rampage. He has pleaded not guilty by reason of insanity.

Prosecutors have argued that Holmes began plotting the attack while enrolled as a neuroscience doctoral student at the University of Colorado's Anschutz Medical Campus, a program he left a month before the mass shooting.

The defense, meanwhile, appears to be focused not so much on what Holmes allegedly did that night but his mental state then and earlier.